1. Field of the Invention
The invention relates to a heater with a glow plug/flame monitor in which, during glow plug ramp time intervals, the amount of energy supplied per unit of time can be successively changed, especially reduced, and with a control unit which is operationally coupled to the glow plug/flame monitor. Furthermore, the invention relates to a motor vehicle which is provided with such a heating device.
2. Description of Related Art
German Patent DE 198 22 140 C1 discloses a process for flame monitoring in a motor vehicle heater in which the resistance value of a glow plug is evaluated, during glow pauses in which there is no power supply voltage on the glow plug, by a control unit for detecting a flame in a combustion chamber. Monitoring takes place by checking whether the glow coils of the glow plug assume a predetermined resistance value within a given time interval.
Published German Patent Application DE 199 03 305 A1 discloses a process for monitoring the flame in a motor vehicle heater which is provided with a temperature sensor or flame monitor which projects into the combustion chamber. The measurement signal of the flame monitor is supplied to a control unit and is evaluated for flame detection depending on a given temperature threshold value and additionally the temperature gradient. With this process, flame-out detection is possible after the starting element, in the form of a flame monitor or glow plug, has been completely turned off.
Existing methods of flame monitoring by means of a glow plug/flame monitor have the disadvantage that during the starting phase, i.e., during glow operation of the glow plug, continuous monitoring of the flame is not possible. This problem arises especially for small heaters up to 5 kW heat output. Extreme smoke emissions can occur to some extent by flame blow-off during the currently unmonitored starting phase.